1. Field of the Invention
The present invention relates to oscillators on integrated chips or circuits within communication devices, and more particularly, the present invention relates to a varactor-based oscillator with quadrature output having a cross-coupled configuration for use in a communication device, such as a wireless networking device.
2. Description of the Related Art
The use of wireless communications for in-home and in-building networks, and direct communications is increasing in popularity. In conventional communication systems, data may be modulated onto at least one radio frequency (RF) carrier frequency and transmitted as a modulated signal. The transceiver receives the RF modulated signal and demodulates the signal to recapture the data. In wireless applications, the data is modulated and transmitted over a wireless network to another location. The wireless device, or user equipment, receives the signal and demodulates it for an application.
Regardless of the communication system or device, a transceiver generally includes an antenna, a filtering section, a low noise amplifier, an intermediate frequency (IF) stage and a demodulator. The antenna receives RF modulated signals and provides the signals to the filtering section. The filtering section may pass the RF signals of interest to the low noise amplifier. The low noise amplifier amplifies the received RF signals of interest and provides the amplified signals to the IF stage. The IF stage may include one or more oscillators, mixers, or adders to step-down the frequency of the RF signals to an intermediate frequency signal, or base- band signal. The IF stage provides the IF, or base-band, signals to the demodulator. Depending upon a particular protocol, algorithm or method, the demodulator demodulates the signals to recapture the data for use in an application.
Some applications may use quadrature output signals from the oscillators. Like normal oscillators, these oscillators seek to output a signal having a specific frequency. Once the oscillator reaches the specified frequency, the oscillator may lock onto the frequency. If the oscillator does not generate the specified frequency, then the oscillator may be adjusted via feedback or other means until the specified frequency is achieved. A ring oscillator may be used having at least two stages to provide the quadrature output. Each stage may have phase shift with an overall phase shift of 360°.
By having two or more stages, a ring oscillator may generate increased noise as well as introduce potential phase shift errors. These actions degrade an output signal and prevent the oscillator from achieving a specified frequency noise. These actions also may prevent an adequate frequency range being generated for use in a variety of oscillation applications. Further, each stage of these oscillators increases delay in providing the output signal to the demodulator. Conventional oscillators may use current control by implementing a voltage-to-current converter to convert the control signal. A control voltage may be applied to the converter that outputs a current control signal to the oscillator. The added component of the converter may increase noise within this particular oscillator.